The present invention relates to insulative polyurethane foams. The present invention particularly relates to polyurethane foams having improved retention of insulative properties.
It is known to prepare polyurethanes by reacting polyisocyanates with active hydrogen containing materials. For example, it is known to combine methylene diphenyldiisocyanate (MDI) or polymeric methylene diphenyldiisocyanate (PMDI) with polyether or polyester polyols to prepare polyurethane foams having good insulative properties. These insulating foams may be found in applications ranging from home construction to ice chests and refrigerators and even to industrial applications such as pipe and vessel insulation.
In addition to good insulative properties, polyurethane foams, particularly rigid polyurethane foams can have other desirable properties. For example, such foams can have good structural properties such as compressive strength, abrasion resistance and dimensional stability upon exposure to temperature and humidity changes. Isocyanurate foams can have particularly good flame resistance. All of these properties are resultant upon a careful choice of formulation components used to prepare the foams.
But preparing polyurethane foams is not always trouble free. Sometimes problems can arise with formulations which do riot have some desired physical property. For example, a foam can have poor flame resistance and a reformulation to correct that problem may be required. Other problems can arise in other areas not directly associated with foam properties. For example, the use of chlorofluorocarbon (CFC) blowing agents has become subject to increasing criticism and regulation due to environmental concerns.
One solution to the use of CFC blowing agents in preparing polyurethane foams has been to use alternative blowing agents such as carbon dioxide and hydrochlorofluorocarbon (HCFC) blowing agents. But such a solution can sometimes be a problem in itself. Use of carbon dioxide and HCFC blowing agents can result in polyurethane foams which can lose some of their insulative properties over time. It would be desirable in the art of preparing polyurethane foams with alternative blowing agents to prepare foams which can retain their insulative properties longer than conventional foams.